Interleukin-33 (IL-33) is a member of the interleukin-1 (IL-1) cytokine family that is encoded by the IL33 gene, and is constitutively expressed in structural cells, such as smooth muscle, epithelial, and endothelial cells. IL-33 can be induced by inflammatory factors in macrophages and dendritic cells. Cellular stress caused by environmental triggers, such as allergens, toxins, and pathogens, can lead to IL-33 release. Bioavailable IL-33 associates with a heterodimeric IL-33 receptor complex composed of suppression of tumorigenicity 2 (ST2) protein and interleukin-1 receptor accessory protein (IL-1RAcP) to activate the AP-1 and NF-κB pathways through the adaptor protein myeloid differentiation primary response 88 (MyD88) and possibly MyD88-adapter-like (Mal) protein. IL-33 stimulates a number of cell types, including innate type II (ILC2) cells, mast cells, basophils, eosinophils, and dendritic cells, to promote Type 2 immunity.
The IL-33 pathway has been suggested to be involved in various diseases, including allergy-related diseases for which there remains a need to develop improved compositions, including therapeutic anti-IL-33 antagonists, and methods for treatment.